Lithographer&#39;s glass



Patented May 5, 1931 a UNITED STATES PATENT OFFICE EDWARD A. ZEH, 0FPASSAIC, JERSEY, ASSIGNOR TO ZEH INCORPORATED, 013

CLIFTON, NEW JERSEY, A COREQRATION OF NEW JERSEY LITHOGRAPHER'S GLASS NoDrawingL provement in the art of lithography and spe-' cifically relatesto a substitute for the lithographic stones and plates now in generaluse and to a method of preparing and using such a substitute,hereinafter referred to as a lithographic glass plate.

In making transfers from lithographic stones as practiced at present, itis the usual practice to place markings on the stone to locate thesuccessively positioned transfer papers andby means of such papersreplaced one after the otheron the stoneto take off duplicateimpressions for use in forming the final color printing plates. Themethod is not conducive to accuracy in the locating of the reproductionson the printing plates due among other reasons to the fact that thetransfer paper frequently sticks to the stones as it is peeled off thesame, and in removing the paper it stretches thus distorting thetransfers. It is vitally necessaryin lithographic Work that thetransfers on the printing plates be exact duplicates of each other toinsure the edge to edge contacting of the different colored areas on thefinal prints.

The primary object of the invention is to provide a form of lithographicstone, or rather a substitute for such a stone, by means of which thetransfers on the several print ing plates can be'made as exactduplicates of each other and thus capable of having their coloredreproductions superposed on each other line for line.

Broadly, this object is attained by using a transparent or rather atranslucent plate prepared to receive the image in place of the usualopaque stone forming the original design thereon by any of the methodsnow- Applicationfiled January 5, 1929. Serial No. 330,630.

substitute which will function efficiently in practicing high gradelithographic and photolithographic Work which will avoid certain defectsat presentknown in the use of lithographic stones and their metallicsubstitutes, and which will possess certain economic advantages in boththe original cost of preparing the same and in storage and othersubsequent cost in practicing the art of reproducing from such opaquestones.

Basically, these objects are attained. by fusing glass colors or enamelin the form of minute articles toa sheet of glass to produce therequisite grain, stipple or roughness of surface, hereinafter referredto as grain in a refinement of texture necessary to produce fine tonesand character in the resulting reproductions. Attempts have been madeheretofore to prepare such articles by grinding or etching or paintingglass to provide the requisite grain, but attempts along these lineshavenot been able to produce a stone capable of use in high grade worksuch as the producing of half tones and the like and such stones whenetched have only a limited use in producing cheap cardboards or billboard sheets are entirely unfited for use in photolithographic work andother Work requiring an. artistic finish.

In lithographic workthere is a demand for lithographic stones which canbe formed of any desirable size; which will give a variety of grain,some fine almost to the point of. be ing smooth and others which willgive a coarse or rough surface effect with different shades ofcoarseness between these two extremesand to provide a stone substitutewhich will possess all of the advantages of the present form of highgrade stone. 7

Accordingly another object of the invention is to provide for arefinement in rough.- ness of surface or working face produced on thestone substitutes herein featured and to provide for a uniformity ofsurface and with any desired degree of roughness and which selection ofdegree and uniformity of surface has not been capable of production byany known method of finishing the stone substitutes or metallic platesnow in general use.

Still another object of the invention is to provide a lithographic stonesubstitute or glass plate which can be produced economically in avariety of colors and which can be produced in sheets, both flat andcurved and which sheets can be readily cut to size after they arefinished to assure identity in the several composite parts.

Various other objects and advantages of the invention will be in partobvious from a consideration of the method features of the disclosure,from the description of one physical embodiment of the invention and inpart will be more fully set forth in the following particulardescription of one method of practicing the invention, and the inventionalso consists in certain new and novel modifications of the preferredmethod and other features of construction and combinations of partshereinafter set forth and claimed.

In practicing the method of forming the plate herein featured, a surfaceof a sheet of glass, preferably clear window or plate glass is cleanedconventionally and to this cleaned surface is applied a layer ofpreviously prepared glass colors, usually a mixture of different colorsand capable of producing minute and spaced apart particles when fused tothe glass. After drying, the coated glass is subjected to one or morefiring operations in an oven or lehr and at a temperature previouslyascertained for this particular work which will fuse the color to theglass without causing the applied color particles to lose'or ratherentirely lose their rough appearance, or differently expressed to becomesmooth.

In preparing the mixture of glass colors there is selected first aningredient which will give the requisite grain to the surface. Zincoxide is usually selected especially as it fuses at a high temperaturebut bone ash can also be used and gives an excellent matted surface.Zinc oxide tends to give a grey cast to the finished glass surface butis the most satisfactory reagent now known despite objections to thegreyness.

It is suggested that the roughness of the Zinc oxide or equivalentreagent be toned down or rendered somewhat smoother by the use of areagent capable of rendering the rough zinc oxide paticles lessnoticeable or prominent on the surface and therefore smoother. Stannousoxide is suggested. especially for this purpose as it fuses at arelatively low temperature and thus assists in bringing the mixture tothe requisite fusing point. Incidentally, the stannous oxide has theeffect of bleaching the grey effect of the zinc oxide. Red lead oxidehas been used in place of the stannous oxide with satisfactary results.

As one specific illustration, a mixture containing forty percent byweight of Zinc oxide, and fifty percent of stannous oxide has been usedwith a suitable glass flux. In this par tieular case, ten percent byweight of a soft lead containing flux was used. Different colors may beadded to give the desired coloration. For instance, in forming the reds,oranges and yellows, a selenium base is used; for forming the blues acobalt is used; all in the proportions necessary to give the requiredintensity and tone of color shade.

In compounding these ingredients, extreme care must be exercised toobtain the proper fusing point. As the composition of glass varies fromtime to time and even different batches of glass purchased from the sameconcern and sold as identically the same glass differ in their fusingpoints, it is necessary to test each batch of glass and each mixture ofthe glass colors above described experimentally before proceeding withthe preparation of the lithographers glass herein featured. It issuggested that a sample of the glass under test he first subjected toascertain its fusing point; then the rough and smooth surface producingreagents in the coating mixture above referred to should be apportionedboth to obtain the desired resulting finish, or rather roughness offinish, and if necessary the grain producing reagents should be combinedwith the requisite amount of flux to bring the fusing aoint of themixture below the fusing point of the particular glass on which it is tobe used. The mixture of reagents so prepared and combined is placed on asmall sample of the glass ant subjected to a heat treatment. Thetemperature is raised experimentally to that point where the mixturefuses into the surface of the glass with a resulting smooth finish. Thisfinish is of course unsuited for lithographic work.

In the instant case recited above this complete smooth finish fusingpoint was found to be eleven hundred and eighty (1180 F.) degreesFahrenheit.

lVith this preliminary work finished it is possible to proceed to formthe lithographic glass. A sheet of plain window glass, plate glass oreven a colored glass sheet is first cleaned on one face followingconventional practices in cleaning glass to receive glass colors. Theprepared mixture preferably in liquid form is sprayed, brushed orotherwise applied to the cleaned surface and in such way that thesurface receives a thin but uniform coat. One way in which this isattained is to spray the sheet from one side to the other by directingthe spray up and down and along vertically extending parallel bands,after which the coating so applied is permitted to dry by exposure toatmospheric air; this usually takes about one minute. Then a second coatis applied, this time directing the spray from top to bottom and alongparallel horizontal hands, after which this second coat is permitted todry. Finally one or more additional coats are applied criss-crosspreferably directing the spray diagonally of the plate and alongparallel bands at forty-five degrees to boththe vertical and horizontalbands forming the firsttwo coats. After each application the coats arepermitted to dry and after the last coat the glass plate is laid downfiat with its coated surface fac ing upwardly and is subjected to anatmospheric drying for a long period of time preferably for at least onehour. It is also suggested that theglass colors be applied to the glasssurface by means of a decalcomania or any of the other methods now usedin applying coating to glass surfaces.

When thoroughly dried the coated sheet is placed in an oven or lehr andsubjected to a heat or firing treatment until the colors have fused intothe glass. At this time particular care is exercised to insure atemperature less than the ascertained temperature at which the colorsbecame smooth. If the colors are underfired the surface is too rough andthe particles do not lie fiat on the glass, and if overfired the surfacebecomes smooth. In most cases a temperature about forty degrees lessthan the temperature at which the colors fuse to a smooth finish isabout right, but here again some experimental tests are necessary inorder to obtain the exact temperature at which the best results areobtained. In the specific caseabove mentioned where zinc and stannousoxides were used a temperature of eleven hundred and forty (1140 F.)degrees Fahrenheit gave satisfactory results.

When thus fused the resulting glass is permitted to cool conventionallyand may be then used for the purpose herein intended. A better characterof surface is provided however by subjecting the surface so formed to arubbing operation with a suitable abrasive and until the desiredsmoothness or rather the desired degree of roughness is attained. Groundflint and pumice stone are the usual abrasives used for this purpose andthe practice followed is that used in polishing smooth glass surfaces.As these plates are usually ordered by sample, the rubbing proceedsuntil the finish on each plate matches that of the sample.

By following the technic herein outlined there is finally produced anall-glass substitute for a lithographic stone comprising a sheet ofglass of any desired thickness having a design, image or patternreceiving surface defined by fused, spaced apart glass or enamelparticles integral with the glass sheet and forming agrained appearanceto the surface.

When viewed at a distance as at arms length the plate produced byfollowing this method seems smooth but with a grained or non-reflectingsurface. When viewed at close range under a low powered reading glassthere is disclosed a uniformally roughened surface.

As the roughened surface so produced is an integral part of the glassbase it is. impossible for the surface to peeled, and it is not affectedby submersion inwater. After the design is photographed or otherwiseim-i posed on the glass plate, the artist can work on the same.conventionally while under water to bring up the high lights and othernecessary retouching for the glass so surfaced is visible under water.With the glass plate so formed the design'may be transferred directly tothe usual zinc and aluminum plates from which the design is printed,incidentally saving the .expense .of effecting the transfer'by means oftransfer paper now necessary-with known forms of lithographic stones.

After once ascertaining the proper fusing point for any one particulargrade or bath of glass, it is obvious that any amount or number ofplates may be practiced simply by coating the plates with the determinedglass color mixture and subjecting the sameto the ascertained fusingtemperature. In producing lithographic plates by this method and as a Ifactory production the cost is very much lower than the nearestcorresponding grade of lithographic stone. As the glass plates preparedas herein disclosed are thin compared to the stones, there is effected amaterial saving instorage space.

.vVhen so'prcpared the frosted grained sur the designs, the plate isused as the negative in a photocomposing machine which permits of adefinite resetting of the plate in case reproductions are to be made atsome future time. The machine is advanced along the large color platesin parallel lines conventionally until the desired number of;reproductions are formed on' the plate of one color and the methodrepeated foreach other color plate desired.- As the glass plate withitsoriginal design is used over and over again without removing any of itsdesign forming coatings, it is obvious that there is no deterioration ofthe design. It is simply subjected to the eflect of light passed throughit at each exposure. As the .reproductions are made following the usualpractices in forming blueprints and like photoprinting each reproductionis an exact duplicate of every other reproduction and there is nopossibility of sectional distortions as is the case with paper transfersand no necessity of exercising care to ascertain that the reproductionswere taken repeatedly from the same parts of the stone.

I claim:

1. In the art of preparing a grained glass sheet for use in place of alithographers stone, the method which includes the steps of applying aglass color to a sheet of glass covering the surface in parallel bands,permitting this first coating to dry, applying a second coat of saidcolor covering the dried surface with parallel bands disposed at rightangles to the first applied bands, permittingthis second coating to dry,similarly applying a third coating in diagonal parallel bands at anangle to both the first two mentioned bands, subjecting the glass socoated to an atmosphere drying for about an hour, subjecting the glassto a heat treatment at a temperature sufficiently high to fuse thecolors to the glass but at a temperature less than that at which thecolors would fuse to a smooth finish to produce a rough grained surface;permitting the glass so treated to cool and rubbing the rough surfacewith an abrasive until a desired fineness of grain surface is attained.

2. In the art of preparing a grained glass sheet for use in place of alithographers stone, the method which consists in applying to a surfaceof glass a coating of a mixture comprising zinc oxide, approximatelyforty percent by weight, stannous oxide, approximately fifty percent byweight and a flux approximately ten percent by weight, and subjectingthe glass so coated to a firing treatment at a temperature of abouteleven hundred and forty degrees Fahrenheit.

3. In the art of preparing a grained glass sheet for use in place of alithographers stone, the method which consists in applying to one faceof a sheet of clear glass a coating comprising a mixture of zinc oxide,stannous oxide and a flux, and subjecting the glass so coated to afiring treatment at a temperature of about forty degrees Fahrenheit,lower than the temperature at which said coating would fuse to a smoothfinish when applied to this particular glass.

4:. In the art of forming a grained glass sheet for use in place of alithographers stone, the method which consists in applying to one faceof a main sheet of clear glass a uniform and thin coating of a glasscolor permitting the same to dry in the presence of atmospheric air,subjecting a sample piece of the same glass and similarly coated anddried to a firing treatment to determine the temperature at which thereis a fusion of the glass colors into this particular glass and at whichascertained temperature there will be formed a smooth finish to thecoated face of the sample glass, subjecting said main coated sheet to afiring treatment at a temperature ap proximately that of said determinedtemperature but slightly less than the same, thereby H to fuse thecolors into the glass and to pro glass will give a less rough or asubstantially smooth effect, together with a flux added to regulate thedesired fusing point of the mixture, coating a sheet of glass with saidmixture, and subjecting the glass so coated to a firing operation and ata temperature sufficiently high to cause the colors to fuse to the glassand. to cause the smooth effect producing color to become smooth orsubstantially smooth, and at a temperature not so high as would causethe rough grain producing color to lose entirely its grain producingeffect or to become smooth.

(5. In the art of forming a lithographic glass plate, the method ofapplying a coating containing zinc oxide uniformally over a surface of aglass plate and subjecting the plate so coated to a firing treatment ata tempera ture sufficiently high to fuse the zinc oxide into the glassand cause the zinc oxide particles to be somewhat flat onthe glass butnot so high as would cause the zinc oxide to become smooth across theface of the resulting glass plate.

7. In the art of forming a lithographic glass plate, the method heretoconsists in applying to a glass surface a coating containing a mixtureof a fine grain producing reagent and coarse grain producing reagent andsubjecting the glass so coated to a firing treatment to fuse thereagents into the glass and thus produce a grained surface having atexture depending upon the relative proportions of the reagents in themixture.

8. I11 the art of providing a grain effect on the surface of alithographers glass, the method which consists in applying to thesurface of a plate of glass, a coating of a mixture comprising Zincoxide, stannous oxide and a flux and subjecting the glass so coated to afiring treatment at a temperature of about forty degrees Fahrenheitlower than the temperature at which said coating would fuse to a smoothfinish on this particular glass and rubbing the resulting surface withan abrasive until the desired grain effect is attained.

9. In the art of forming a grained glass sheet for use in place of alithographers stone, the method which consists in applying to one faceof a sheet of clear glass a uniform coating of a glass color, permittingthe same to dry, subjecting a sample piece of the same glass andsimilarly coated and dried to a firing treatment to determine thetemperature at which there is a fusion of the glass colors into thisparticular glass and at which temperature there will be formed a smoothfinish to the coated face of the sample glass, subjecting said coatedsheet to a firing treatment at a temperature approximately that of saiddetermined temperature but slightly less than the same, thereby to fusethe colors into the glass and to provide a ground or rather grainedsurface effect in distinction from the smooth finish of the sample,permitting the glass sheet so treated to cool and rubbing the grainedsurface with an abrasive until the desired fineness of grained'elfect isattained.

10. A substitute for lithographic stone, comprising a sheet of glasshaving a design, image or pattern receiving surface defined by fused,spaced apart glass color particles integral with the glass sheet lyingflat thereon and forming a somewhat smooth grained and non-reflectingsurface when reviewed at arms length and which discloses a uniformlyroughened appearance when closely examined.

Signed at New York city, in the county of New York and State of NewYork, this 8rd day of January A. D. 1929.

EDWARD A. ZEH.

